1. Field of the Invention
The present invention relates to a wrench, especially to a ratchet wrench that is applied in unidirectional.
2. Description of the Prior Art
With reference to FIG. 12, a conventional ratchet wrench disclosed in U.S. Pat. No. 7,111,529 comprises a head (40), a tapered coil spring (44), a retractable jaw member (45) and two cover plates (46). The head (40) has a front end. An opening (41) is defined in the front end of the head (40) and has a peripheral surface, a first side and a second side. Multiple recessions are formed on the peripheral surface of the opening (41) at intervals. The recessions are used for providing ratcheting space when rotates a bolt in a backward direction. Respectively corresponding to the first side and the second side of the opening (41), a first jaw (42) and a second jaw (43) are formed on the head (40). The second jaw (43) has an inner surface. A slot (431) is defined in the inner surface of the second jaw (43) and has an inner end. Two recesses are defined in two sides of the second jaw (43) and communicate with the slot (431). The tapered coil spring (44) is mounted in the slot (431) and has an outer end. The retractable jaw member (45) is mounted in the slot (431) and has a side surface. The retractable jaw member (45) abuts against the outer end of the tapered coil spring (44) and projects into the opening (41). The two cover plates (46) are respectively attached to and close the recesses in the second jaw (43).
When using the conventional ratchet wrench, the peripheral surface of the opening (41) and the side surface of the retractable jaw member (45) engage a head of a bolt. The head of the bolt has multiple flats and multiple corners formed between adjacent flats. In order to tighten the blot, a torque is applied to the blot head with a turning stroke in a forward direction. Rotating the conventional ratchet wrench in the backward direction is necessary for tightening the blot. When the head (40) is rotated in the backward direction about the head of the bolt, the retractable jaw member (45) will be, pressed into the slot (43) by the flats of the bolt head to disengage the jaw member (45) from the blot head. Thus, the head (40) would be ratchetingly rotated in the backward direction to a position suitable for next turning stroke in the forward direction. Repeating backward and forward rotations allows tightening the bolt without removing the conventional ratcheting wrench from the bolt.
Although the conventional ratchet wrench can tighten bolts with a series of sequential backward and forward rotations, the conventional ratchet wrench still has following problems.
1. In order to mount a resilient member in the narrow slot (431), a tapered coil spring (44) is used as for abutting the retractable jaw member (45). It is also appreciated by an artisan with general knowledge in the field that the tapered coil spring (44) may also be replaced with a resilient member having features and functions similar to that of the tapered coil spring (44). In addition, the tapered coil spring (44) is characterized by occupying less space when compressed. Using the tapered coil spring (44) allows the slot (431) to be made shallower and smaller than using a normal coil spring to miniaturize the conventional ratchet wrench. The tapered coil spring (44), however, takes a cost much more than a normal coil spring does. It is observed in the field that there is a need for a ratchet wrench suitable for miniaturizing and employing a low-cost coil spring.
2. In order to mount the tapered coil spring (44) into the slot (431), the inner end of the slot (431) has to be formed at a right angle. Precise casting process, linear cutting process or LASER cutting process would be necessary for making such structure, and this significantly raises manufacturing cost for the convention ratchet wrench. The cutting process for forming the slot (431) may be preceded after a different cutting process for forming the opening (41) with a central machine tool. Consequently, precision for forming the ratchet wrench is reduced due to the aforementioned two individual cutting processes.
3. In order to provide sufficient retracting space for the retractable jaw member (45), the slot (431) must have an enough depth. The second jaw (43) needs to have a thick thickness for defining a deep slot (431). Otherwise, the structural strength may not be strong enough to prevent failure.
4. With the aforementioned thick thickness of the second jaw (43), miniaturizing the conventional ratchet wrench would be impossible. As a result, the application of the conventional ratchet wrench is extremely limited, especially is not applied for small bolts.
5. The retractable jaw member (45) of the conventional ratchet wrench retracts in a linear movement travel, so the side surface of the retractable jaw member (45) projects out from the recession (431) and provides only a small area for contacting the bolt head. Such structure causes unexpected and unsafe slipping during use. Since no extra space is available for the side surface due to the linear movement of the retractable jaw member (45), the conventional bolt is not applicable for bolts slightly different in sizes.
6. Two projections (432) may be formed on the bottom of each recess for connecting with a corresponding cover plate (46). When attaching the cover plates (46) to the recesses, the projections (432) are melted and welded with the cover plates (46). However, visible welding marks appear on and around the cover plate (46) with such a welding process. Furthermore, the structural strength of combination of the cover plates (46) with the recesses is not enough for bearing a shock to cause cover plates (46) escaping from the recesses.
To overcome the shortcomings, the present invention provides a ratchet wrench to mitigate or obviate the aforementioned problems.